Characteristics of metabolism and function of the neural retina (NR) and pigment epithelium (PE) are studied in cultured cells and in freshly dissected tissue. Several new neurotransmitter/neuromodulator receptors have been identified in retina, pigment epithelial cells, and retinoblastoma cells in culture. Human retinoblastoma cells have been successfully maintained in monolayer culture. They can be differentiated into neuronal or glial cell types, depending on the culture conditions.